At present,GNSS-Acoustic(GNSS-A)combined technology is widely used in positioning for seafloor geodetic stations.Based on Sound Velocity Profiles(SVPs)data,the equal gradient acoustic ray-tracing method is applied in ...At present,GNSS-Acoustic(GNSS-A)combined technology is widely used in positioning for seafloor geodetic stations.Based on Sound Velocity Profiles(SVPs)data,the equal gradient acoustic ray-tracing method is applied in high-precision position inversion.However,because of the discreteness of the SVPs used in the forementioned method,it ignores the continuous variation of sound velocity structure in time domain,which worsens the positioning accuracy.In this study,the time-domain variation of Sound Speed Structure(SSS)has been considered,and the cubic B-spline function is applied to characterize the perturbed sound velocity.Based on the ray-tracing theory,an inversion model of“stepwise iteration&progressive corrections”for both positioning and sound speed information is proposed,which conducts the gradual correction of seafloor geodetic station coordinates and disturbed sound velocity.The practical data was used to test the effectiveness of our method.The results show that the Root Mean Square(RMS)errors of the residual values of the traditional methods without sound velocity correction,based on quadratic polynomial correction and based on cubic B-spline function correction are 1.43 ms,0.44 ms and 0.21 ms,respectively.The inversion model with sound velocity correction can effectively eliminate the systematic error caused by the change of SSS,and significantly improve the positioning accuracy of the seafloor geodetic stations.展开更多
Pure nitrogen gas was heated with direct current arc, at input powers from several hundred Watt to over 5 kW, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating ...Pure nitrogen gas was heated with direct current arc, at input powers from several hundred Watt to over 5 kW, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km/s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.展开更多
Autonomous and Remotely-operated Vehicles(ARVs)rely on precise underwater navigation via integrated Ultra-Short Baseline(USBL)acoustic positioning system and Strap-down Inertial Navigation System(SINS).However,spatiot...Autonomous and Remotely-operated Vehicles(ARVs)rely on precise underwater navigation via integrated Ultra-Short Baseline(USBL)acoustic positioning system and Strap-down Inertial Navigation System(SINS).However,spatiotemporal variations in underwater Sound Speed Profle(SSP)degrade USBL performance,reducing overall navigation accuracy.This study proposes a novel in-situ SSP correction scheme for SINS/USBL integration.We analyze SSP temporal variation with the USBL positioning scheme to build a Two Dimensional(2D)temporal SSP model;then derive partial derivatives(based on equal-gradient ray-tracing)to quantify the displacements from azimuth,incident angle,and propagation time errors;and fnally develop an adaptive two-stage information flter to estimate sound speed perturbation and detect USBL outliers.Simulations and South China Sea trials are conducted to verify its efectiveness.Compared with the traditional tight-coupling method,root mean square errors are reduced from 0.45m and 0.23 m with the traditional tightly-coupled method to 0.08 m and 0.07 m with the in-situ SSP correction scheme,representing improvements of 82.2%in the north and 69.6%in the east directions,respectively.Experimental results demonstrate that the proposed method efectively estimates the sound speed disturbance in real time,thereby signifcantly improving the performance of tightly integrated inertial-acoustic navigation systems.展开更多
By constructing an innovation decision-making model that includes economic policy uncertainty(EPU),this paper finds that EPU will have a negative impact on corporate innovation.Further analysis shows that it has asymm...By constructing an innovation decision-making model that includes economic policy uncertainty(EPU),this paper finds that EPU will have a negative impact on corporate innovation.Further analysis shows that it has asymmetric effects on long-term and short-term innovation decisions and puts forward two potential mechanisms of inhibitory effect in long-term:one is reducing follow-up investment,and the other is reducing marketization return.The empirical analysis verifies the inhibitory effect of EPU on corporate innovation and verifies two potential mechanisms.We further investigate the potential moderating effects:increased information transparency and of capital structure adjustment speed can mitigate the inhibition of EPU on corporate innovation.This study provides clear policy implication to ease the uncertainty of economic policy at the government level.展开更多
基金National Natural Science Foundation of China(Nos.41931076,42174020)Laoshan Laboratory(No.LSKJ202205101)State Key Laboratory of Geo-Information Engineering(No.SKLGIE2020-M-1-1)。
文摘At present,GNSS-Acoustic(GNSS-A)combined technology is widely used in positioning for seafloor geodetic stations.Based on Sound Velocity Profiles(SVPs)data,the equal gradient acoustic ray-tracing method is applied in high-precision position inversion.However,because of the discreteness of the SVPs used in the forementioned method,it ignores the continuous variation of sound velocity structure in time domain,which worsens the positioning accuracy.In this study,the time-domain variation of Sound Speed Structure(SSS)has been considered,and the cubic B-spline function is applied to characterize the perturbed sound velocity.Based on the ray-tracing theory,an inversion model of“stepwise iteration&progressive corrections”for both positioning and sound speed information is proposed,which conducts the gradual correction of seafloor geodetic station coordinates and disturbed sound velocity.The practical data was used to test the effectiveness of our method.The results show that the Root Mean Square(RMS)errors of the residual values of the traditional methods without sound velocity correction,based on quadratic polynomial correction and based on cubic B-spline function correction are 1.43 ms,0.44 ms and 0.21 ms,respectively.The inversion model with sound velocity correction can effectively eliminate the systematic error caused by the change of SSS,and significantly improve the positioning accuracy of the seafloor geodetic stations.
基金supported by the National Natural Science Foundation of China(Nos.11575273 and 11475239)
文摘Pure nitrogen gas was heated with direct current arc, at input powers from several hundred Watt to over 5 kW, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km/s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.
基金National Natural Science Foundation of China(42304040,42174020,42174021)National Key Research and Development Program of China(No.2024YFB3909700,2024YFB3909702)+3 种基金Shandong Province Natural Science Foundation(ZR2023QD081,ZR2025MS643)National Key Laboratory of Spatial Datum(No.SKLSD2025-KF-16)Fundamental Research Funds for the Central Universities(No.24CX06045A)Qingdao Natural Science Foundation(23-2-1-65-zyyd-jch,23-2-1-217-zyyd-jch).
文摘Autonomous and Remotely-operated Vehicles(ARVs)rely on precise underwater navigation via integrated Ultra-Short Baseline(USBL)acoustic positioning system and Strap-down Inertial Navigation System(SINS).However,spatiotemporal variations in underwater Sound Speed Profle(SSP)degrade USBL performance,reducing overall navigation accuracy.This study proposes a novel in-situ SSP correction scheme for SINS/USBL integration.We analyze SSP temporal variation with the USBL positioning scheme to build a Two Dimensional(2D)temporal SSP model;then derive partial derivatives(based on equal-gradient ray-tracing)to quantify the displacements from azimuth,incident angle,and propagation time errors;and fnally develop an adaptive two-stage information flter to estimate sound speed perturbation and detect USBL outliers.Simulations and South China Sea trials are conducted to verify its efectiveness.Compared with the traditional tight-coupling method,root mean square errors are reduced from 0.45m and 0.23 m with the traditional tightly-coupled method to 0.08 m and 0.07 m with the in-situ SSP correction scheme,representing improvements of 82.2%in the north and 69.6%in the east directions,respectively.Experimental results demonstrate that the proposed method efectively estimates the sound speed disturbance in real time,thereby signifcantly improving the performance of tightly integrated inertial-acoustic navigation systems.
文摘By constructing an innovation decision-making model that includes economic policy uncertainty(EPU),this paper finds that EPU will have a negative impact on corporate innovation.Further analysis shows that it has asymmetric effects on long-term and short-term innovation decisions and puts forward two potential mechanisms of inhibitory effect in long-term:one is reducing follow-up investment,and the other is reducing marketization return.The empirical analysis verifies the inhibitory effect of EPU on corporate innovation and verifies two potential mechanisms.We further investigate the potential moderating effects:increased information transparency and of capital structure adjustment speed can mitigate the inhibition of EPU on corporate innovation.This study provides clear policy implication to ease the uncertainty of economic policy at the government level.
